Electrophoretic printing using source sheet containing an adsorbent material



March 5, 1968 D. .1. J. LENNON 3,372,102

ELECTROPHORETIC PRINTING USING SOURCE SHEET CONTAINING AN ADSORBENT MATERIAL Filed Jan. 16, 1964 FIG. I

INVENTOR.

DONALD J. J. LENNON ATTORNEYS ttes Patent s v t. r

fifice 3,372,102 ELECTROPHORETIC PRINTING USING SGURCE SHEET CONTAWING AN ADSGRBENT MA- TERHAL Donald J. J. Lennon, Acton, Mass, assignor to The 'Carters Ink (Jompany, Cambridge, Mass, a corporation of Massachusetts Filed Jan. 16, 1964-, Ser. No. 338,245 5 Claims. (Cl. 204-181) ABSTRACT OF THE DISCLOSURE In electrophoretic printing ionizable dye particles are retained on an adsorbent material until an electrical field is applied to cause them to be transferred in the printing operation.

This invention relates to electrophoretic printing and more particularly to an improved source sheet for use in electrophoretic printing.

Electrophoretic printing is described in the United States Patent application of Gerald Oster, Ser. No. 152,579, filed Nov. 15, 1961 now US. Patent No. 3,145,- 156. In general, it includes a source sheet incorporating ionizable dye particles. When this surface of the source sheet is placed in surface-to-surface contact with a recipient sheet and moistened with an appropriate liquid to ionize the dye particles, an electrical field of appropriate polarity applied across the sheets will cause the ionized dye particles to transfer from the source sheet to the recipient sheet, printing the receipient sheet. The pattern printed on the recipient sheet may be controlled, for example, by shaping the moistened area, the applied electrical field, or by placing a stencil between the sheets.

In practice, it has been found that when such source sheets are placed on one another for any length of time, as when they are packaged together, should the dye particles become ionized by, for example, the sheets absorbing moisture, they tend to migrate and transfer to the surface of the adjacent sheet, milking the surface of dye particles and contaminating the adjacent sheet. Also, if'dye particles ionizing to opposite charges are present, they tend when ionized to migrate towards one another, or precipitate, and negate one anothers charges. This too materially decreases the quantity of dye particles available for electrophoretic printing.

The primary object of this invention is to provide a source sheet in which the dye particles will not readily migrate when ionized, but from which ionized dye particles will readily transfer to the adjacent surface of a recipient sheet in liquid phase therewith under the influence of an electric field. This and other objects of the invention will be apparent from the following description of a preferred embodiment of the source sheet.

The source sheet of the present invention includes an adsorbent material having ionizable dye particles adsorbed thereon. The adsorptive force binds the dye particles to the adsorbent material and impedes migration of the dye particles when ionized. During electrophoretic printing, the surface of the source sheet containing the adsorbed dye particles is placed in contiguous liquid phase with the surface of a recipient sheet, the liquid ionizing the dye particles, and an electrical field is applied across the sheets to overcome the adsorptive force and cause the ionized dye particle to transfer to the recipient sheet.

A preferred embodiment of the invention will be further described in connection with the accompanying drawings in which:

FIG. 1 is a schematic representation of a particle of adsorptive material having dye particles adsorbed thereon; and

FIG. 2 is a schematic representation in cross-section of a simple arrangement of electrodes and source and recipient sheets arranged for electrophoretic printing.

In accordance with the principles of the invention, it has been discovered that unwanted migration of ionized dye particles, either towards one another or from the source sheets to adjacent sheets, may be substantially eliminated by adsorbing the charged dye particles on an adsorptive material, and coating, impregnating, or otherwise securing to the cellulose fibers of the source sheet an adsorptive material on which the dye particles have been adsorbed. The material with adsorbed dye particles may be added to the paper slurry during formation of the source sheets, if desired. Appropriate adsorptive materials include adsorptive grade carbon black, charcoal, alumina or silica gel. The dye particles, either anionic or cationic, or both, may be of a single type, or a mixture of various types of dye particles. Appropriate dyes are set forth in Table l of the Oster application supra.

A particle of adsorptive material 1 is schematically illustrated in FIG. 1. On it have been adsorbed dye particles 2, schematically indicated by cross signs. The adsorptive force between the adsorptive material 1 and the dye particles 2 binds the dye particles to the adsorptive material and prevents their random migration from the adsorptive material.

The dye particles conveniently may be adsorbed on the particles of adsorptive material by first forming a slurry of the adsorptive particles in a liquid, and then adding the dye particles to the slurry until substantially the maximum amount of dye is adsorbed by the adsorptive particles. For example, a slurry may be made from adsorptive grade finely ground carbon black particles and water. This slurry will appear black due to the carbon particles, but around the meniscus, the carbon particles are discernible. The dye particles are added slowly, either as a dry powder or as a solution, and the slurry of carbon black particles containing dye particles shaken or thoroughly stirred as the dye is added until the water around the meniscus begins to take on the tinge of the dye. At this point, the adsorptive carbon black particles will have adsorbed substantially the maximum quantity of the dye particles. More dye will be adsorbed if the slurry is first allowed to sit for a while, and then more dye particles are added. However, this final bit of dye tends to migrate and readily separate from the adsorptive particles, which is not desirable.

The quantity of dye adsorbed by the particles is dependent on many factors, among which are the size of the adsorptive particles and the dye particles, the ionic characteristics of the dye, the chemical characteristics of the dye, and the liquid used to form the slurry. The various factors effecting adsorption are discussed at length in volume five of a series titled Technique 'of Organic Chemistry, published in 1951 by Interscience Publishers,

Inc. of New York, NY. Volume five, by H. G. Cassidy,

is titled Adsorption and Chromatography. By correlating these factors, the adsorption characteristics of the dye and adsorbent particles may be balanced against the desorption characteristics during electrophoretic printing to achieve the desired printed dye intensity while minimizing the tendency of the adsorbed dye particles to migrate over a period of time either to oppositely charged dye particles or to adjacent sheets when ionized.

The adsorbent material with the adsorbed dye particles may be coated or impregnated on the surface of the source sheet or incorporated into the paper during the papermaking process, or it may be deposited on the source sheet in a selected pattern by printing or writing the material onto the source sheet. As shown in FIG. 2 and described in detail in the Oster application supra, during electrophoretic printing, the surface of a source sheet on which the adsorbent material with its dye particles 2 have been deposited is placed in contiguous fluid phase with the surface of a recipient sheet 4, as by wetting the contacting faces with water, to ionize the dye particles. Sheet electrodes 5 and 6 are placed over the outer surface of the source and recipient sheets, and a source of direct electric potential 7 connected between the electrodes to apply an electric field of the appropriate polarity and magnitude across the sheets. This field overcomes the adsorptive force and causes the adsorbed ionized dye particles to be transferred to the surface of the recipient sheet, which is thereby printed. Thus normally the dye particles are held by the adsorptive particles to the source sheet. They will transfer only after they have been ionized, and an appropriate electric field applied to them. They have no tendency to naturally migrate.

To illustrate the principles of the invention, the maximum quantities of the following dyes were adsorbed on carbon black, which in turn was deposited on a source sheet for electrophoretic printing.

The adsorbed dyes on the source sheets showed no substantial tendency to migrate, even when purposely ionized. When oppositely ionizing dyes No. 3 and No. 4 were deposited on the same source sheet, they also showed substantially no tendency when ionized to migrate together, or precipitate. The source sheets were used in electrophoretic printing, and excellent transfer of the dyes to the recipient sheet was obtained.

As a specific example illustrative of the invention, 9 grams of carbon black was mixed with 100 cc. of water to form a slurry. To this slurry was slowly added 1 gram of Acilan Ponceau 3R-Color Index No. 16255 dye, at which point the meniscus began to take on the tinge of the dye, indicating that the carbon black particles had adsorbed substantially the maximum quantity of the dye particles. A sheet of paper was dipped into this slurry, and then dried. The dye showed no tendency to migrate when ionized. When this source sheet was used in electrophoretic printing, excellent transfer of the dye to the recipient sheet was obtained.

The dyes listed above are only exemplary of those which may be employed in electrophoretic printing. It is to be understood that any other ionizable dye, such as those listed in Table I of the Oster application supra, also may be used, either singly or in combination with one another. When used in combination with one another, the adsorbent particles carrying different adsorbed dyes may be mixed and applied to the source sheet without fear of the dyes precipitating and migrating together. If the dyes were not adsorbed, they would have to be separately applied to the sheet, or they would precipitate.

While carbon black was used as the adsorptive material in the examples given above, other adsorptive materials, such as those listed previously, also may be used either alone or in combination with one another. The colorless adsorbents, such as alumina or silica gel, may be employed to advantage where it is desired to remove all of the adsorbent dye particles by electrophoresis and leave a substantially colorless area on the source sheet. Alternatively, dyes of different color and relative printing mobility may be adsorbed on such colorless adsorbents and one dye removed from a selected area of the source sheet by electrophoresis to leave a corresponding area of a different color on the source sheet.

Since the carbon black and charcoal are black and absorb light completely, the natural black color of such adsorbents may be utilized to completely conceal the color of the dye or dyes adsorbed thereon. These particles may be used in ordinary black or white printing processes, and the genuineness of the article printed with such particles may be ascertained by retrieving the adsorbent dye or dyes by electrophoresis. After ascertaining the genuineness of such printed sheets, the carbon particles would remain black and the printing will not be rendered illegible or distorted. Dyes of different polarity or mobility may be adsorbed together on the material used in an ordinary printing process. Any selected dye could be withdrawn by electrophoresis from the printed sheet by selecting the correct polarity and duration of the applied electrical field to thereby retrieve different quanta of information. Also, by adsorbing dyes of different colors on the adsorbent material, multi-color printed images can be obtained.

Adsorbent particles carrying adsorbed dye or dyes may be included in the paper-making process, and the resultant source sheet subsequently coated with a layer of cellulose fibers. After ionizing the adsorbed dye particles of such a source sheet, the ionized dye particles could be transferred by electrophoresis to the surface of the source sheet, producing an image, or even to the surface of a recipient sheet in fluid contact with the source sheet, printing it.

While preferred embodiments of the invention have been described, it is to be understood that various modifications may be made within the scope and spirit of this invention.

I claim:

1. A process of electrophoretic printing which comprises providing a source sheet having at one surface a fluid phase containing an adsorbent material having ionizable dye particles adsorbed thereon, placing a recipient sheet in surface-to-surface contact with said surface of the source sheet and in contiguous fluid phase with said adsorbed ionized dye particles, and applying an electrical field across said sheets to cause said adsorbed ionized dye particles to be transferred to the recipient sheet to print the recipient sheet.

2. A process as set forth in claim 1 in which the ionizable dye particles are adsorbed on carbon while not substantially varying the appearance of the carbon. 3. A process as set forth in claim 1 in which the adsorbent material is substantially colorless and dyes of different colors and mobilities are adsorbed thereon, whereby removal of a selected dye leaves a different colored image on the source sheet.

4. A process of electrophoretic printing which comprises providing a source sheet having at one surface a fluid phase containing an adsorbent material having ionizable dye particles of different relative characteristics including color, mobility and electrical charge adsorbed thereon, the color of the adsorbent material dominating and concealing the dye particles, the dye particles and adsorbent material being disposed on said source sheet in selected patterns, placing a recipient sheet in surface-tosurface contact with said surface of the source sheet and in contiguous fluid phase with said ionized dye particles, and applying an electrical field across said sheets of se- 5 lected polarity and intensity for a selected interval to cause a selected group of said ionized dye particles to be transferred to the recipient sheet whereby the pattern of a selected group of dye particles is transferred to the recipient sheet.

5. A process as set forth in claim 4 in Which an electrolyte saturates the adsorptive surface of the source sheet and the recipient sheet to provide said contiguous fluid phase.

6 References Cited UNITED STATES PATENTS 3,145,156 8/1964 Oster 204180 5 HOWARD S. WILLIAMS, Primary Examiner.

JOHN H. MACK, Examiner.

E. ZAGARELLA, Assistant Examiner. 

